set some properties in AST Node ctor - workaround microsoft/TypeScrip…

…t#26811

src/language-html/ast.js

@@ -7,6 +7,21 @@ const NODES_KEYS = {
 
 class Node {
   constructor(props = {}) {
+    /**
+     * define some class properties here, to work around
+     * https://github.com/microsoft/TypeScript/issues/26811
+     */
+    this.index = undefined;
+    this.siblings = undefined;
+    this.prev = undefined;
+    this.next = undefined;
+    this.parent = undefined;
+
+    this.name = undefined;
+    this.namespace = undefined;
+    this.hasExplicitNamespace = undefined;
+    this.children = undefined;
+
     for (const key of Object.keys(props)) {
       const value = props[key];
       if (key in NODES_KEYS) {